CBS News reports that “Russian hackers struck at the heart of the U.S. military in August 2015 by seizing the e-mail system used by the Joint Chiefs of Staff, CBS News has learned.”

“Then-Chairman of the Joint Chiefs Martin Dempsey was alerted to the attack by an early-morning phone call from the Director of the National Security Agency, Admiral Mike Rogers.”

“Now retired, Dempsey told CBS News in an exclusive interview that the attack was proceeding at an alarming speed. Within an hour, hackers had seized control of the unclassified e-mail system used by the Pentagon’s Joint Staff, the organization of some 3,500 military officers and civilians who work for the Chairman.”